Unit 8: Part 2: Fertilization/Development and Human Reproduction

Key Questions 1. Why is sexual reproduction advantageous over asexual reproduction? 2.What structures make up the male and female reproductive systems? 3. How do offspring of sexually-reproducing organisms receive their genetic information?

Key Questions 4. Why do the offspring look different from the parents? 5.What controls human reproduction and development? 6. How does a zygote develop and what factors can affect its development?

Question??? Why is sexual reproduction advantageous over asexual reproduction?

Reproductive Systems Goal of male and female reproductive systems is to create gametes, deliver them, and in females, to allow for embryonic and fetal development.

Compare the Gametes EGGSSPERM Non-MotileMotile LargeSmall Yolk/Cytopla sm Nucleus Head/ Nucleus Tail Neck

Human Egg Cell

Bat sperm (mitochondria ) Human Sperm

Human Reproduction Comparison of male and female reproductive anatomy

Female Reproductive System 2 Functions of the female reproductive system: 1.To produce eggs. 2.To provide an environment for internal fertilization and development of embryo.

Female Reproductive System FYI: –Facts: Females have about 2 million eggs at birth. 400,000 eggs survive to puberty. Only 450 – 500 eggs mature and leave the ovaries.

Female Reproductive System StructureFunction Ovaries1.Produce eggs 1.Secrete sex hormones (estrogen and progesterone) Follicles1.Tiny egg sacs where eggs mature within the ovaries.

Female Reproductive System StructureFunction Fallopian Tubes (Oviduct) 1.Tube that egg travels through from ovary to uterus. 2. Where fertilization occurs!!! (within 48 hrs of egg release) Uterus1.Thick muscular organ 2. Where fertilized egg develops until birth

Female Reproductive System StructureFunction Cervix1.Muscular tube between uterus and vagina Vagina1.Also called birth canal 2. Connects uterus to outside the body.

Male Reproductive System Main function of the male reproductive system: 1.Produce and deliver sperm.

Male Reproductive System StructureFunction Testes1.Has small coiled tubes-seminiferous tubules – where sperm cells are produced. 2. Produce testosterone-necessary for sperm production. Scrotum1.Contains the testes 2. Temperature is 1-2 degrees cooler than body – provides “optimal” environment for sperm production.

Male Reproductive System StructureFunction Epididymis1. Where sperm mature (takes about 18 hours) after leaving seminiferous tubules and are stored. Vas Deferens1.Tubes that leave each of the testes and join the urethra.

Male Reproductive System StructureFunction Urethra1.Tube leading to outside of male body. 2. Both semen and urine pass through this tube. 3.Semen traveling through penis = land adaptation for internal fertilization.

Male Reproductive System SystemFunction Prostate gland Seminal Vesicles Cowper’s Gland 1.Secrete fluids into the urethra when sperm pass through - transport medium for sperm. Semen1.Mixture of sperm + seminal fluids = semen mL of semen released-contains 400 million sperm.

Reproductive System Spermatogenesis Video –(on server-40 sec.)

What is the role of the menstrual cycle???

Human Menstrual Cycle Feedback mechanism regulated by interaction of various glands and hormones Cycle begins at puberty (around age ) Cycle stops during pregnancy and at menopause (age 45-55)

Human Menstrual Cycle Egg is prepared matures and released from ovary; uterus prepares to receive it (if fertilized) There are 4 stages of the menstrual cycle

Human Menstrual Cycle Stage 1 Follicle Stage FSH – Follicle stimulating hormone 1. FSH is secreted by pituitary gland to stimulate 1 follicle to mature an egg. Estrogen 1. Estrogen is secreted by the follicle. 2. Causes vascularization (uterine lining thickens with a rich supply of blood vessels)

Human Menstrual Cycle Stage 2 OvulationLH – Luteinizing Hormone 1.High level of estrogen (from follicle makes pituitary gland decrease FSH level 2. As level of FSH decreases, pituitary gland secretes LH (luteinizing hormone). 3. Ovulation – high level of LH causes the release of an egg from follicle in ovary

Human Menstrual Cycle Stage 3 Corpus Luteum Stage Progesterone1.Corpus luteum (empty follicle that fills in with fluid/cells) secretes progesterone 2. Progesterone maintains the vascularization of the uterus.

Human Menstrual Cycle Stage 4 Menstruation1.Occurs when fertilization does NOT take place. 2. Shedding of the uterine lining caused by decrease in progesterone levels 3. Low progesterone levels cause pituitary to start with FSH production – starts all over again

Menstrual Cycle es/hormones/horm4.cfm?age=Age%20ran ge% &subject=Biologyhttp:// es/hormones/horm4.cfm?age=Age%20ran ge% &subject=Biology

Golden Ticket Name the female reproductive system structures the sperm need to travel through to get to an egg (hint: there are 4).

The joining of the gametes…

Fertilization: Fusion of of gametes to produce a zygote. Zygote: A fertilized egg Reproduction

Fertilization + fertilization 1n 2n Zygote Fertilization RESTORES the chromosome number (2n)

Zygote

Fertilization Eggs are NON-MOTILE (don’t move on their own), so sperm must find the egg. –A fluid environment is necessary so sperm can swim to the egg.

Internal Fertilization Gametes fuse inside the female’s body. Occurs in terrestrial (land) environment.

FYI – External Fertilization Gametes join outside of the female’s body in an water environment so sperm can swim to eggs Large number of gametes (eggs) released to be sure some will survive (No parental care after birth)

External Fertilization

Embryonic Development: Define Development: –Orderly series of changes that occur in an organism. –In humans, development occurs inside the female’s body

Development Zygotes undergo a series of early mitotic cell divisions called CLEAVAGE. Once cleavage begins, the zygote is considered a developing embryo.

Development 2 cells 4 cells 8 cells

Development Early stages of cleavage results in a solid ball of cells called a MORULA. Draw: A solid ball of cells

Development They are re-arranged into a HOLLOW BALL of cells 1 cell thick called a BLASTULA. Draw: The middle has been ‘blasted out’

Stem Cells Up until this point in the embryo’s development, the cells are referred to as stem cells. The cells have not become specialized yet – they are all the same.

Stem Cells Video (13:40) (on server – stem cell research) – cells-research.htmlhttp:// cells-research.html

Development When the blastula reaches hundreds of cells, 1 side indents to form a 2-layered embryo called a GASTRULA.

Development The process of indentation is called GASTRULATION. Outer layer is called ectoderm Inner layer is endoderm Draw: ectoderm endoderm

Video Clips Fertilization (on server-1 min.) Differentiation (on server-2 min.)

Development After the endoderm and ectoderm form, a middle layer forms between them called the MESODERM. Draw: ectoderm mesoderm endoderm

Development FYI- Endoderm, mesoderm, and ectoderm are embryonic layers, or GERM LAYERS.

Development Differentiation: Occurs during gastrulation. –Cells become special kinds of cells to do certain jobs (specialization) (no longer stem cells) – genes turn on/off –The 3 germ layers give rise to various tissues, organs, and systems.

Differentiated Cells

Development FYI: Ectoderm – hair, skin, nails, nervous system Mesoderm – bones, muscles, circulatory system, excretory system, reproductive system Endoderm – Digestive system, respiratory system, liver, pancreas

Development For proper development, the embryo needs nourishment, oxygen, proper temperature, protection, and waste removal.

FYI Many organisms have external development. –Occurs outside the female’s body. Nourishment comes from yolk in egg. Little or no protection. Example: frogs, fish

Jawfish Male jawfish care for eggs in his mouth until they hatch

Chick - 9 days 1. The clear fluid surrounding the chick is the amnion. 2. The yellow area covered with a blood system is the yolk. 3. The blood system in the piece of egg shell is the allantois. 4. The milky, clear material to the right of the shell is albumen.

Human Embryonic Development Human females have specialized structures to allow for internal development.

Internal Development –After fertilization, the dividing by mitosis embryo travels from fallopian tube to uterus –Implantation - embryo embeds itself in think uterine lining (marks beginning of pregnancy – occurs 5-10 days after fertilization) Differentiation begins to occur – cluster of cells from inner cell mass becomes embryo rest becomes surrounding tissues Pregnancy tests test for HCG

Internal Development Special structure forms called a PLACENTA – formed to nourish embryo and remove wastes. Allows for exchange of nutrients, wastes, gases between mom and embryo by process of DIFFUSION.

Internal Development There is NO DIRECT CONNECTION between mom and embryo’s blood streams. UMBILICAL CORD – structure that attaches embryo to placenta. –Blood vessels (2 arteries and 1 vein) in cord transports blood back and forth from embryo and placenta

Placenta

Umbilical Cord Blood Banking blood/umbilical-cord-stem-cellshttp:// blood/umbilical-cord-stem-cells

Problems… Placenta previa

Internal Development Amniotic Fluid – –Liquid within a membrane that protects embryo/fetus (water, salts, cells, urine from baby). –Gives it a stable environment and absorbs shock

Early Development The early stages of development are very important – external factors can disrupt development at this time –Environmental factors such as inadequate diet, use of alcohol/drugs/tobacco, other toxins, infections can harm embryonic development

Fetal Development After 8 weeks of development = fetus During months 4-6, fetus becomes more complex and specialized Last 3 months – systems mature and fetus grows in size and mass Gestation –length of time from fertilization to birth (40 weeks in humans – about 9 months)

Fetal Development

Internal Development Child Birth –About 9 months after fertilization –Complex factors trigger process Hormones released by pituitary gland (oxytocin) triggers uterus to contract –Causes cervix to open –Amniotic sac may break –Labor – Baby is delivered head first Umbilical cord is clamped and cut Mother delivers placenta

Problem… Cesarean section Umbilical cord around baby’s neck (25%)

After Birth After birth, mother produces a hormone (prolactin) which stimulates production of milk in mother’s breast tissues The nutrients found in breast milk have everything the baby needs for growth and development in early life

Internal Development FYI- b.Non-Placental Mammals –Internal fertilization and development in uterus (no placenta). –Young are born prematurely – then crawl into pouch-attach to mammary glands.

Internal Development Development is completed in pouch “Survival of the fittest.” Examples – Marsupials (pouched mammals) kangaroo, opossum

Non-placental mammals: marsupials Wombat

Other - Twins Identical Fraternal

Other-Twins Siamese/Conjoined Twins

Other Reproductive Technologies

Applicable NYS Learning Standards 2.1e, 3.1g, 4.1c, 4.1d, 4.1e, 4.1f, 4.1g, 4.1h